Circulating system for pulp digesters



Aug. 4, 1931. D. B. DAVIES CIRCULATING SYSTEM FOR PULP DIGESTERS Filed Aug. 18,, 1928 17:12:? 2.1 Dav-6d B..Dau'zl as.

Patented Aug. 4, 1931 CIRCULATING SYSTEM FOR PULP DIGESTERS Application filedlAuglst 18, 1928. Serial No. 800,433.

UNITED STATES PATENT OFFICE 7 DAVID B. DAVIES, or SHELTON, wnsnrne'ron V This invention relates to a circulating sys-. tem for pulp digesters and more particularly to'an apparatus and method for obtaining rapid circulation of digester liquor during the .5 process of cooking chipsv for the preparation ofsulphite; pulp. V

1 In the so-called Ritter-Kellner orquick cooking process, after the digester is filled with chips and acid, direct steaming of the contents of-the digester is started in the usual way. In the case of large digesters, especial: ly, andto some extent in the case of smaller digesters. It is extremely difficult to effect a uniform rise of temperature throughout the contents of the digester during the heating up period. Furthermore, actual cooking of the chips does not effectually begin until all parts of the digester contents'reach 110 to 120 6.: and any time wasted in bringing this temperature about is a loss to-the entire cook, since the last portions to reach cooking rem perature govern the finishing of the cook. Moreover, uneven temperature in different parts of thedigester result in pulp lacking .2 in uniform qualities and in lower yields;

In some instances, pumps and other mechanical divices have been employed to effect circulation 'of the digester liquor, but such devices are costly to maintain and get out of 9 order. frequently.

'It is therefore an obj ect of this invention to provide an apparatus for circulating digester liquor having no moving parts and capable of effecting a rapid circulation within the 3 digesterto insure rapid heating and uniform temperatures throughout. ."Other'. and further important objects of this invention will be apparent from the dis-.

closures in the specification and the'accompanying drawing. 1

This invention (in a'preferred form) is illustrated in the drawing and hereinafter more fully-described. a

On the drawing: 7 Thedrawing is an elevational View of a pulp digester showing a circulating system installed thereon, with parts broken away and in section.

The reference numeral 1 indicates a vertical stationary digester-of standard type such as is used in cooking by the sulphite process with direct steam. The auxiliary tank 2, according to the principles of this invention, is connected to the upper portion of the digester 1 by means of a pipe line 3 entering said auxiliary tank as at i. A perforated strainer 14 serves to protect the opening ofthe pipe 3 into the digester 1 to pres vent chips from getting into said pipe line 3.

A second pipe line 5 connects the lower portions of the digester l and auxiliary tank 2. A Valve 6 is positioned in the pipe line 3 conveniently close to the digester, and a check valve 26 near the tank 2, Said pipe line 5 is likewise provided with a valve 7 and a check valve 15, the latter being inserted in the line 5 between the valve 7 and the tank 2 to prevent a reverse flow of liquor from the digester 1 into the tank 2. The auxiliary tank 2, which may be of any desired shape or size, is preferably positioned on a level with the lower portion of the digester. Said tank 2 is built to withstand the usual steam pressures in a sulphite mill and is lined with acid resistant brick 8, Or the like. A steam line 9 enters the top of the auxiliary tank 2 as at 10 and is provided with a valve ll for controlling the steam flow. A check valve 16 is inserted in the steam line 9 between the valve 11 and the opening 10 in the tank to prevent an accidental flow of liquor into the line 9 should the steam pressure therein at any time fall below the digester pressure while the valve 11 is open.

The exhaust line 12, also connected near the top of the tank 2 is provided with a relief or poppet valve 13 for exhausting the gas pressure within said tank.

During the steaming of the digester to bring the contents up to cooking temperatures, circulation of the digester liquor within the digester is effected by the operation of my circulating system as follows: Keeping the other valves closed, the valve 6 is opened to permit liquor from the digester to enter the tank 2 through the pipe line 3 and check valve 26 until the pressures in the digester and tank are equalized. As soon as the tank 2 is filled with digester liquor, valve 6 is closed and valves 7 and 11 are opened.

' through the Steam under higher pressure than that Within the digester 1 is thus introduced through the steam line 9 into the top of the auxiliary tank 2 and by virtue of its greater pressure will force the liquor contained therein out pipe 5 into the bottom of the digester 1. As soon'as the entire body of the digester liquor is discharged from the tank 2, valves 7 and 11 are closed and the poppet valve 13 opened to bring the interior of the tank 2 again to atmospheric; pressure. The cycle is then repeated as before. 7

The check valve 26 automatically prevents steam or liquor from passing out of the tank I Qthrough the pipe line 3'and the check valve similarly prevents a reverse flow through the pipe 5. Accordingly it is possible to keep both valves-6 and 7 open during the entire circulating operation and'rely'entirely upon the check valves 15 and 26 automatically opening and closing in accordance with the fluctuation of pressure within the tank 2.

. It will be understood that the opening and closing of the valves 11 and 13 may be automatically controlled, as an automatic timing device, or may be partially or wholly controlled by a float device within the tank2. Furthermore it will beunderst-ood that in place of the steam'used to discharge the di-' gester liquor from the auxiliary tank 2,.hot

gas relieved from another digester at higher pressure than the digester being steamed may A be employed.

The tank 2 may, if desired,

'l'ation will cause uniform temperature in the digester rapidly to an equal temperathroughout the "digester independently of the irregular; absorption of heat during the steaming process. 7

The use of my circulating system is thus seen to provide a rapid and uniform circulation of the digester'liquor throughout the digester durlng the cooking process. The

system gives unlimited circulation of the cooking acid and thus brings the whole mass ture, resulting in a much more uniform grade of pulp and in higher yields.

I amaware that many changes may be made and numerous details of construction may be varied through a Wide range without departing from the principles of this invention, and

I, therefore, do not purpose'limiting the patent granted hereon otherwise tated by the prior art.

I claim as iny'invention: 5 1. A liquor circulating system for pulp dithan necessigesters, comprising in combination with a digester, an auxiliary container, valve controlled connections from said container to said digester, exhaust means on said container and a fluid pressure connect-ion to said container for forcing liquor fromsaid container into said digester.

I 2. A liquor circulating system for pulp digesters, comprising in combination Witha digester, an auxiliary tank positioned below the liquor level in said digester, valve-controlled connections from said tank to said digester at points near the top and bottom of said digester'respectively, an exhaust valve on said tank and a steam line connection opening into the top of said'tank for forcing liquor from said tank into said digester.

' 8; The method of circulating liquor in pulp digesters, which comprises allowing a portion of the liquor from near the top of a digester to flow into an auxiliary chamber intro'ducing steam under'greater pressure than exists in said digester into said chamber to force said portion into the lower part of said digester, and exhausting the steam from said chamber. V

4. The method of circulating liquor in pulp digesters, which comprises intermittently allowing a portion of the liquor from near the top of "a digester during the steaming of the digester to flow by reason of the pressure within the digester into an auxiliary chamber, introducingsteam under greater pressure than exists insaid digester into said chamber to force said portion into the lower part of said digester, and exhausting the steam from said chamber.

5. The method of circulating liquor in pulp digesters, which comprises allowing a portion of the liquor from onepart of the digester during the heating up of the contents of the digester to flow into an auxiliarychamber subjecting said portion of liquor in said auxiliary chamber to higher direct steam pressure than exists in said digester to force said liquor portion into another part of said digester and thereby obtain uniform heating up of the contentsof said digester, and exhausting the steam from said chamber.

f 6} The method of circulating liquor in pulp digesters; which comprises allowing a portion of the liquor from one part of the di gester during the heating up of the contents of the digester to flow into an auxiliary chamber and subjecting said portion of liquor in said auxiliary chamber to-higher direct steam pressure than exists in saiddigester toforce said liquor portion into another part of said digester and thereby obtain-uniform heating up of the contents of said digester, bringing the pressure insaid auxiliary chamber back to atmospheric and repeatingthe cycle.

. 7. The method of circulating liquor in pulp digesters, which comprises intermittently allowing a portion of the liquor near the top of pressure.

DAVID B. DAVIES. 

